The proposed study is designed to characterize, by in vitro methods, the collateral vessels that develop in response to chronic femoral artery occlusion with respect to innervation, autonomic receptors, and reactivity to naturally occurring vasoactive agents in an attempt to elucidate a possible stimulus for the selective growth of collaterals. These characteristics of collateral vessels will be compared to those of normal branch arteries of similar size, from the same hypotensive extremity and from the unoccluded normotensive extremity during the period of active collateral growth and when collateral growth is complete. The following characteristics of collateral arteries, normotensive branch arteries, and anterior tibial arteries from both the hypotensive and normotensive extremities will be evaluated: 1. Regulation of neuronal activity by presynaptic receptors including evidence for and activity of alpha adrenergic, beta adrenergic and cholinergic presynaptic receptors. 2. Identification and quantification of the alpha adrenergic postsynaptic receptor with a radioligand (3H-dihydroergocryptine) of high specific activity and the effects of competing ligands (receptor agonists and antagonists) on the binding of the radioligand. 3. Role of calcium in vascular smooth muscle determined by the effects of extracellular calcium concentration as the fast and slow components of contraction, on 45Ca uptake and on 45Ca efflux. 4. Effects of hypothermia on reactivity to norepinephrine, KCl, CaCl2 and acetylcholine, affinity of NE (KA) and phentolamine (pA2) for the alpha receptor, and disposition of neurotransmitter after inhibitors of Uptake1 (cocaine), Uptake2 (normetanephrine), or metabolism (U-0521 and iproniazid).